hargitt: pennaria tiarella and tubularia crocea. 173 



resulting in x- and v-shaped figures. The spindle becomes radial, the 

 asters are lost, though the centrosomes remain, and the first polar cell 

 is formed. There is some evidence that before the second maturation 

 spindle forms, the chromatin remaining in the egg reorganizes into a 

 nucleus with a definite membrane, the chromatin taking on the con- 

 dition typical of the so-called resting stage. A second maturation 

 spindle and a second polar cell are formed. The chromosomes re- 

 maining in the egg form the egg nucleus. This is usually composed 

 of several distinct vesicles, which may fuse at once or remain distinct 

 till the time of conjugation with the sperm nucleus. 



3. Fertilization. — When spermatozoa are present inconsiderable 

 numbers, they may entirely surround the living egg, but nearly always 

 they appear to be more plentiful at one or two places than elsewhere. 

 In some of the living eggs a very definite cone on the surface of the egg 

 was seen at the place where the spermatozoa were most abundant, 

 and in several cases there were apparently two cones present in one 

 egg, spermatozoa being collected about both of them. Whether the 

 cone is a true " cone d'attraction " or a "cone d'exsudation" (Fol, '79) 

 could not be determined on account of the impossibility of ascertaining 

 whether it was formed before or after the entrance of the spermato- 

 zoon. An entrance cavity, such as was found in coelenterates by 

 Metschnikoft' and by Brauer, I have never seen. After the medusae 

 were liberated, the eggs sometimes retained their position on the 

 manubrium. When, in such cases, spermatozoa were present in the 

 water, some of them gained access to the ova, for sections of such eggs 

 showed that fertilization had occurred under these circumstances. It 

 is probable that the tissues surrounding the eggs had been ruptured 

 before the spermatozoa gained access. 



Hargitt (:00) speaks of a sort of "convulsive surface torsion" of the 

 egg of Pennaria soon after the spermatozoon enters, and I, too, found 

 that under the same conditions the surface of the egg became irregular, 

 and then after a short time apparently rounded out again. Sections 

 show that about the time of entrance of the spermatozoon the cyto- 

 plasm is extremely active; protuberances are extended from many 

 points of the surface of the egg, some rounded, others elongated. 

 Some of these seem to become entirely detached, whereas others are 

 apparently withdrawn. Somewhat later, when conjugation of the 

 germ nuclei is about to occur, the surface of the egg as a rvde appears 

 regular and smooth. 



As has already been stated, the polar cells arise before the eggs are 

 discharged, and hence usually before the spermatozoon enters. In a 



